Distribution of bulk and unsolicited e-mail to randomly selected mail clients for purposes of mainly advertising or soliciting is becoming increasingly problematic for mail clients. Moreover, in a system where a mobile phone is a mail client, there is the added problem of the mail client incurring unnecessary costs since communication charges for receiving e-mails are paid by the owners of mobile phones that are the recipients of such e-mails. To counter the problem of bulk and unsolicited mail, measures to prevent their distribution have been proposed.
For example, Japanese Patent Application Laid-Open Publication No. 2003-115925 proposes a technique where a source address of an e-mail is extracted and counted. If a number of e-mails sent from an identical source address to a mail box within a predetermined time period becomes equal to or greater than a predetermined threshold number, a determination is made that the mails are unsolicited and are consequently deleted from the mailbox. However, in a large organization such as a corporation, it is not unusual for hundreds or thousands of e-mails to be received during the course of a single day for business communication. Moreover, it is now common practice for publications such as newsletters to be simultaneously bulk-distributed to a large number of subscribers. Under such circumstances, if as described above a predetermined threshold is used to determine whether e-mail is unsolicited, a genuine e-mail may be prevented from being received by the intended recipient.
In view of the problem described above, Japanese Patent Application Laid-Open Publication No. 2003-46578, for example, proposes a technique for determining if a number of e-mails sent from an identical source address exceeds a certain threshold number. In the case that the threshold is exceeded, it is determined whether the addressee of the mails wishes to receive the mails, and if not so, the mails are deleted from the mail box. However, making such determinations is complicated and time-consuming for users.